Research On Thermal Performance And Heat Transfer Mechanism Of Spherical Phase Change Unit Heat Storage Device

Solar heating has the advantages of being clean,environmentally friendly and harmless,but also has the disadvantages of being intermittent and unstable.In practical engineering applications,thermal storage technology is one of the effective ways to overcome these disadvantages and improve energy efficiency.The phase change thermal storage unit has a direct impact on the heat transfer efficiency of the thermal storage system,and the heat transfer performance of the thermal storage system is related to the structure of the phase change unit,and a more efficient phase change energy storage system can be achieved by improving the structure of the phase change unit.In this paper,to improve the heat transfer performance of the heat storage device,the Phase Change Material(PCM),whose main material is paraffin,is encapsulated into each spherical phase change unit,and the heat transfer performance of the spherical phase change unit heat storage device is investigated experimentally and simulated numerically by changing various variables while controlling the total mass of PCM remains the same.Based on this,the studies are as follows.(1)Five different diameters of phase change unit physical φ70,φ50,φ46,φ38,φ25 and eight different diameters of phase change unit physical models φ70,φ65,φ60,φ55,φ50,φ46,φ38,φ20 are designed.the study shows that: the smaller the diameter of phase change ball,the higher the heat storage/exhaust efficiency of heat storage device but the increase gradually decreases,according to the comprehensive performance optimal According to the principle of optimal overall performance,φ50 andφ46 are selected as the optimal diameters;with the increase of inlet flow rate and the increase of temperature difference between Heat Transfer Fluid(HTF)and PCM,the storage/exhaust efficiency of heat storage device gradually increases.(2)Three types of heat storage devices with varying layer spacing were designed:bottom-to-top layer spacing of 116 mm,108 mm,93 mm,and 78 mm;each layer spacing was 98.75 mm;bottom-to-top layer spacing was 78 mm,93 mm,108 mm,and 116 mm.The study showed that the heat storage/exhaust efficiency increased or decreased from bottom-to-top compared with the same layer spacing of heat storage devices.A small increase or decrease.(3)Three thermal storage devices with different porosity of 82.9%,72.36%,and 89.03%were designed.It is shown that as the porosity increases,the HTF perturbation around a single phase change sphere increases,and the heat transfer rate between HTF and PCM increases,the higher the heat storage/exhaust efficiency of the heat storage device.(4)The physical and mathematical models of the heat storage device are established based on the phase change heat transfer theory,and the heat transfer process of PCM is analyzed by combining the melting characteristics of spherical units,liquid phase rate cloud and temperature cloud,and the phase change heat transfer mechanism of HTF and PCM with time is investigated.This study uses a combination of experiments and simulations to analyze the thermal performance and heat transfer mechanism based on spherical phase change unit heat storage devices,and designs a variety of spherical phase change heat storage devices with high engineering application value,which lays a theoretical and experimental foundation for the future application and optimization of solar heating systems.